It is now widely accepted that anatomically modern humans (Homo sapiens) emerged in Africa around 200 ka (ka=thousands of years before the present), as evidenced by now-classic hominid sites in eastern Africa and supported by genetic variations among modern populations. Despite the unquestioned African origin of our species, the time when modern humans first exited Africa and the order in which they colonised the remaining continents is hotly debated.

The most recent of these discussions has centred on the timing of the first exodus and its relationship with Quaternary climate variations1. This is clearly a subject that touches a wider and perhaps more complex topic such as the relationship between the evolution and behaviour of humans and their changing environment. This is an appealing subject which bears not only scientific relevance, but also deep cultural implications. For instance, the extent to which climate variability or other environmental drivers has influenced human migrations is a question that stresses the role of geography over culture.

Homo sapiens remains dating back to 125 ka during Marine Isotope Stage 5e (MIS 5e) have been found in modern day Israel. The commonly accepted view is that these remains represent an early human dispersal that failed to spread outside of the Middle East, becoming extinct soon after it stepped out of Africa. The peopling of Europe, Asia and Australasian was supposed to have occurred much later from a single “successful” migration around 70-60 ka1.

However, this view of a single successful migration is being challenged. In 2015, several modern human remains dated to at least 80 ka were found in the Fuyan Cave in southern China2. These findings followed a series of other surprisingly old human fossils in Asia, yet no remains of modern humans older than 50 ka have been found in Europe. This new evidence questioned the classic single “out of Africa” model, suggesting an alternative scenario where H. sapiens expanded eastward into Asia in one or more waves of migration starting well before 70 ka. While it is still unclear what prevented an early migration into Europe.

Back in 2013, Larrasoaña and collaborators combined a series of continental and marine records from northern Africa to propose what is, without question, an exciting idea for any Quaternarist: that orbital-driven Northern Hemisphere insolation played an important role in the migrations of hominids out of Africa3. It has long been noted that the 23-ka precession cycles are clearly imprinted on the Northern Hemisphere summer insolation between 300-60 ka. Every 23,000 years, decreased precession and corresponding high Northern Hemisphere summer insolation are linked to a northward shift of the Intertropical Convergence Zone. These shifts were, in turn, linked to northward expansion of the tropical belt bringing periods of intensified monsoon rainfall over northern Africa and the Middle East. During these humid intervals, the deserted regions of the Northern Africa, the Middle East and the Arabic Peninsula were transformed into savanna-like regions boasting freshwater lakes and extensive grasslands, becoming transient corridors for modern human populations to migrate out of Africa.

Exit passages for African H. sapiens were therefore opened with “orbital” regularity at around 130 ka (MIS 5e), 105 ka (MIS 5c), 82 ka (MIS 5a) and 60 ka (MIS 4-3). Thus it is not surprising that the earliest human fossils out of Africa found in Israel date back to MIS 5e. Furthermore, all the following wet intervals coincide with dated H. sapiens sites in Northern Africa, the Middle East or the Arabian Peninsula. There are several possible routes that the H. sapiens could have taken. The Sinai Peninsula in northern Africa was the most logical passage to exit Africa (Figure 1). However, there is an alternative southern route which connects eastern Africa with southern Asia via the narrow straits of Bab-El Mandeb and Hormuz. This route could have briefly been opened before the sea level rise associated with MIS 5e.

Figure 1 – Homo sapiens emerged in Africa around 200 ka. The older Homo sapiens remains outside of Africa are found in today’s Israel and date back to 125 ka during Marine Isotope Stage 5e. The timing and routes of the first expansion into the other continents is still in debate. For more information see: Stringer, C. (2003).

In an article published just last month, Timmermann and Friedrich (2016) take the idea of precession-controlled wet periods as a pacemaker for human dispersal and test it by running a human dispersal model4. Their new model, forced by environmental variables such as climate variability, sea level changes and the extension of deserts, is able to reproduce a series of independent migration pulses between 110-60 ka in broad alignment with the orbital moist intervals and the archaeological record of Northern Africa (Figure 2). By reproducing the dates for the first arrival time of H. sapiens in places like South China (100-70 ka), New Guinea and Australia (60 ka), and the Americas (14-10 ka), this new simulation provides new weight towards orbital variations as a key driver of early migrations of H. sapiens.

Although the early exodus and multiple orbital dispersal model looks promising, several other issues need to be addressed in future investigations. For instance, the model presented by Timmermann and Friedrich indicates that H. sapiens stepped into Europe between 100-80 ka. This time is at odds with the archaeological record, which shows no evidence for modern humans before 45 ka. Interestingly, the authors suggest the possibility that the first H. sapiens populations in Europe where assimilated by the prevalent Neanderthal population before 50 ka. This hypothesis seems plausible considering the information provided by the recently-cracked genome of Neanderthals which gives hints of the incorporation of modern human genes into European Neanderthals DNA at around 100 ka5.

Together, Quaternary scientists, archaeologist and geneticists are providing exciting new information about past links between climate variability and ancient migrations. An active role of environmental variability in the distribution of modern humans across the globe has long been dismissed by paleo-anthropologists, ethnographers or linguistics who traditionally favoured cultural explanations over “geographic or climatic determinism” to account for ancient human migrations. Nonetheless, a bio-geographic approach to the peopling of the planet seems to be gaining ground. What it is perhaps even more fascinating to any Quaternarist is that a look at the Northern Hemisphere insolation curve shows that the potential number of humid events in Africa and the Middle East over the last 2 million years is in the order of thousands. Future paleoclimate studies and a more complete archaeological record will have the potential to test the role of climate events in the diaspora of previous hominid species as well as the emergence of our own species.

The 2016 AQUA Biennial meeting, in Auckland New Zealand, 5 – 9th December 2016 is rapidly approaching. This meeting, with the theme Quaternary perspectives from the city of volcanoes is shaping up to be our best ever, with some exciting Keynote speakers and about 110 people submitting Abstracts. More details about the conference, held in Old Government House in downtown Auckland, can be found at https://www.niwa.co.nz/climate/research-projects/climate-present-and-past/Aqua2016. Early bird registration continues until October 25.

The AQUA biennial meetings are relatively informal and particularly aim to encourage students and early career researchers to present the results of their research. The meetings definitely showcase the diversity of the Australasian Quaternary community and research.

The Executive Committee of the Australasian Quaternary Association (AQUA) is pleased to announce that they will offer up to six Travel Grants of up to $500 each (AQUA reserves the right to vary the amount and/or number of Grants that it awards) to support attendance at the Auckland 2016 AQUA Biennial meeting.

In the past the AQUA “student travel prizes” have subsidised the attendance of postgraduate students and ECR (<5 years since graduation): we have recognised that some members of the Australasian Quaternary community do not always have the means to attend meetings and hence we have broadened the criteria and in particular added a ‘needs’ component to the eligibility. Awardees of the Travel Grants are expected to have submitted an Abstract (for either a talk or a poster) at the AQUA Biennial Meeting and to write a short article for Quaternary Australasia after the meeting.

So: we invite students, postdocs and other members of the AQUA community to apply for one of these Travel Grants. To be eligible you need to:

1) be a current financial member of AQUA;

2) fill out an application form (available on the AQUA website’s Awards page),

3) send us proof that you have submitted an Abstract and registered for the AQUA conference.

All applications will be assessed on the basis of academic merit and benefit to the recipient but the Executive Committee will also consider need as a criteria. (This latter criterion might include being unemployed, the lack of support from their host institution, or the lack of funding to attend the conference. Active contributors to the Australasian Quaternary community are more likely to be eligible. Having a continuing position at an institution will probably discount you from this component of the Grants.)

The profound and permanent anthropogenic imprint on the planet and the accelerated rate of environmental change has opened a lively debate about establishing a new human-made geological epoch: the Anthropocene. Widely covered in by the public media, the Anthropocene Working Group has officially recognized that human impacts on the environment are of sufficient scale to be considered as a new geological time and agreed that such time started at AD 1950 with the global-wide spike of radionuclides resulting from atmospheric nuclear bomb testing.

Figure 1. The beginning of the Anthropocene at AD 1950 as proposed by the Anthropocene Working group. Figure modified from Waters et al (2016)6. For more information regarding the Anthropocene Working Group visit: http://www2.le.ac.uk/offices/press/press-releases/2016/august/media-note-anthropocene-working-group-awg

Significantly for Quaternary scientists, recent paleoclimate investigations proved to be important in defining the onset of the Anthropocene epoch. At the end, these investigation provided evidence to refute proposed pre-instrumental dates as the starting point for this new epoch, helping to tip the balance towards AD 1950 as the best candidate. Early last year, Lewis and Maslim (2015) reviewed the history behind the concept of an Anthropocene epoch in the Journal Nature1. Considering the formal criterion for defining a geological epoch; that is, the existence of a global-scale signature in stratigraphic material, the authors proposed two specific dates or “golden spikes” for the initiation of the Anthropocene: AD 1610, associated with the collision of the old and new worlds; and AD 1964, associated with the great acceleration of industrial production.

In favor of AD 1610, Lewis and Maslim (2015) listed a series of evidence for global environmental change at around that time, including minimal atmospheric CO2 concentrations in Antarctic ice cores and the presence of exotic fossils markers in sediment sections as new crops and animals started to be exchange between continents. Furthermore, based on a series of articles published between 2008 and 2011, the authors suggested that the drop in atmospheric CO2 recorded in Antarctic ice cores between AD 1580 and 1650 (Figure 2) was caused by an increase in the terrestrial CO2 uptake resulting from a large-scale forest expansion in previously cultivated lands across the Americas. This reforestation followed the dramatic decline of indigenous populations due to socio-political upheaval, famine and disease, brought about by European colonization and exploitation. In other words, Lewis and Maslim (2015) suggested that human activities were behind the CO2 and temperature decline during the coldest part of the Little Ice Age.

A human-driven cooling during Little Ice Age turned out to have wider implications because recent studies have shown that changes in atmospheric CO2 over the last millennium were sourced in the terrestrial biosphere and not in the oceans2. This evidence further opened the enticing possibility that major events in human history over the last 1,000 years could have produced minor -albeit global- variations in atmospheric carbon dioxide3. All these events occurred several centuries before what it is generally accepted as the onset of global anthropogenic impacts, and certainly well before AD 1950.

However, it has long been noted that the net flux of CO2 between the atmosphere and the terrestrial ecosystem is not only controlled by the rate of vegetation uptake (termed primary production), but also by the emissions of CO2 from animals, fungi and some microorganisms (termed terrestrial respiration). Thus, any drop in Atmospheric CO2 could be caused either by an increase in primary production or by a shutdown of the terrestrial respiration.

Bearing these principles in mind, an article published in Nature Geosciences this month4 challenged the suggestion of a human-induced drop in CO2 during the Little Ice Age. Interestingly, this new study did not focus directly in carbon dioxide but on Carbonyl Sulfide (CAS), an organic molecule also present naturally in the atmosphere. Like CO2, CAS is removed from the atmosphere by the terrestrial vegetation. Yet, unlike CO2, CAS is permanently incorporated into plant metabolism and not emitted back to the atmosphere. In other words, atmospheric CAS is a direct measurement of the primary plant production. Rubino et al (2016)4 shows that low concentrations of CO2 during the Little Ice Age are contrasted by an increase in the concentrations of CAS (Figure 2). These opposite changes are a strong indication that a reduction –not an increase- in plant uptake occurred during the Little Ice Age. A CO2 decrease induced by large-scale forest regeneration is therefore unlikely because vegetation re-growth would have dropped CO2 and CAS simultaneously. Instead, the results are consistent by a proportionally larger decrease in the terrestrial respiration (which reduce CO2 emission but does not affect CAS concentration).

The new study of Rubino et al (2016) points to the fact that cooling in the earth system rather than human activities were behind the CO2 decline during the Little Ice Age. In other words, this new study provides evidence against the proposition of AD 1610 or any previous date as the “golden spike” for the beginning of the Anthropocene, adding indirect support to AD 1950 as the best date for the beginning our current epoch.

Figure 2. Upper: atmospheric CO2 concentration recorded in during the little Ice Age in the ice core record of Law Dome, Antarctica4. Lower: Carbonyl Sulfide (CAS) concentration anomaly relative to pre-industrial values4. Figure modified from Rubino et al (2016)4.

All these recent studies highlight how important paleoclimatic and paleoecological research is to our overall understanding of the current trends of the earth systems. As showed in a recently published revision of the industrial-era warming this month5, the entire instrumental time series are immersed into a long-term warming ramp, making instrumental data too short to fully investigate the drivers and structure of the current warming trend.

Formal definitions do not change tangible anthropogenic impacts; neither do they change future scenarios of environmental change, and therefore a debate over when did precisely the Anthropocene began may not be of any significant relevance for the general public. However, the footprints of human activities are now undeniably global and certainly will be detectable for thousands of years to come. Establishing a starting date for the Anthropocene not only has scientific relevance but also social and political implications for the way we understand our relationship to the environments around us – which we invariably depend upon. For example, agreeing that the Anthropocene starting point occurred earlier than the 19th industrial revolution would have effectively dismissed the accelerated modern industrial scale of greenhouse gas emissions since AD 1950, and their associated global warming impacts. The proposed definition of the Anthropocene will need to be ultimately recognized by the International Commission on Stratigraphy (ICS), a process that might be argued over several years.